Query the encoding of the response object

To set the encoding of response object, the method response.setEncoding() is available. What is the method available to query the response encoding.

Tried to list all the methods supported by response object using the following code

    for (var i in proxy_response) {
        console.log(i);
    }

which outputs

_readableState
readable
domain
_events
_maxListeners
socket
connection
httpVersionMajor
httpVersionMinor
httpVersion
complete
headers
rawHeaders
trailers
rawTrailers
_pendings
_pendingIndex
upgrade
url
method
statusCode
statusMessage
client
_consuming
_dumped
req
setTimeout
read
_read
destroy
_addHeaderLines
_addHeaderLine
_dump
push
unshift
isPaused
setEncoding
pipe
unpipe
on
addListener
resume
pause
wrap
setMaxListeners
emit
once
removeListener
removeAllListeners
listeners

None of the methods listed seem to query the encoding type. How to query the response encoding type ?